Hydraulic jack for use in garage

ABSTRACT

A hydraulic jack is provided whose lift arm may be lowered at two different speeds, that is, high and low speeds. Release valves having low and high discharge capacities are interposed between a working oil supply and discharge passages of a hydraulic cylinder for lifting and lowering the lift arm, and in response to partial depressing of a foot pedal the low-discharge release valve is first opened, and when the foot pedal is fully depressed, both of the low and high discharge release valves are opened so that the working liquid under pressure may be discharged selectively in small and large quantities from the hydraulic cylinder.

Umted States Patent 11 1 [111 3,740,952 Fujii June 26, 1973 [54] HYDRAULIC JACK FOR USE IN GARAGE 1,799,298 4/1931 Jakob 60/52 HA 2,145,014 l/1939 Rosenberry 60/52 HB [761 Invent 3 2,211,479 8/1940 Pomeroy 60/52 HA Mltsu-lkenaml 2,319,125 5/1943 Gl'Otc 60/52 111) Kagamlhara, Japan 2,381,553 8/1945 Mott 137/629 [22] Filed: Dec. 21, 1971 Primary Examiner-Edgar W. Geoghegan 1 1 pp 210,326 Attorney-Saul Jecies Foreign Application Priority Data ABSTRACT Dec. 24, 1970 Japan /1 16682 A hydraulic j is Provided Whose lift am y be ered at two different speeds, that is, high and low [52] U.S. Cl /477, 60/481, 91/449, speeds. Release al s ha ing low and high discharge 137/601, 137/628 capacities are interposed between a working oil supply 511 1111. c1. FlSb 15/22 and discharge p g of a hydraulic cylinder for lift- [58] Field of Search 60/52 HB, 52 HA, s n l g the lift arm, and in response to partial 60/52 H1), 477, 479, 431; 91/449; 137/623 depressing of a foot pedal the low-discharge release 629, 601 valve is first opened, and when the foot pedal is fully depressed, both of the low and high discharge release [56] References Cit d valves are opened so that the working liquid under UNITED STATES PATENTS pressure may be discharged selectively in small and 1,706,309 5 1929 Miller et a1. 60/52 HA large quammes from the hydrauhc cylmder' 1,720,434 7/1929 Pedersen 60/52 HA 8 Claims, 7 Drawing Figures 94 s N I 1 95 i 9 103 Y x 8 PAIENIEDJIJIZS I15 3. 740. 952

SIEH 1 U 7 mm NW :9 mm

. mm mm IQ INVFTNTOR.

Yasuhiro FUJII BY Saul Jecies PAIENIEUJIIIIZB ms 3. 740.952

INVENTOR.

Ya suhiro FUJII BY Saul Jecies PAIENIEDJUNZG i975 smut? INVENTOR.

Yasuhiro FUJII BY Saul Jecies.

PATENIEDJIINZS ms 3.740.952

INVENTOR. Ya suhiro FUJII BY Saul Jecies HYDRAULIC JACK FOR USE IN GARAGE BACKGROUND OF THE INVENTION The present invention relates generally to a hydraulic jack, and more particularly to a hydraulic jack for use in a garage, the jack being of the type in which a lift arm and hence a bearing plate can be controlled in re sponse to the extended length of a ram of a hydraulic cylinder mounted upon a carriage.

In a hydraulic jack of the type described, the working liquid under pressure is forced into the hydraulic cylinder mounted upon the carriage to extend the ram so as to raise the lift arm and hence the bearing plate. To lower the bearing plate, the working oil under pressure introduced into the hydraulic cylinder must be returned to a reservoir or the like in order to withdraw or retract the ram. In a prior art hydraulic jack of the type described, only one release valve is interposed between a working oil supply and discharge passages, and is opened when a pressure release foot pedal is depressed, to return the working oil under pressure in the hydraulic cylinder to a reservoir or the like. This means that the working liquid under pressure in the hydraulic cylinder is returned to the reservoir or the like at a flow rate which is determined by the load applied to the bearing plate and by the degree of opening of the release valve. As a result, the speed at which the bearing plate is lowered is uniquely determined by the opening area of the release valve. Therefore, when the opening of the release valve is increased, the bearing plate lowering speed is increased accordingly. This is not desirable when it is desired to lower the bearing plate gradually to a desired position even though this arrangement is preferable for lowering the bearing plate rapidly to the carriage. On the other hand, when the opening area of the release valve is increased, the bearing plate lowering speed may be reduced so that the adjustment of the height of the bearing plate can be much facilitated. But it then takes a long time before the bearing plate is lowered to the carriage. Theoretically it is possible to adjust the bearing plate lowering speed as needs demand by adjusting the stroke of the pressure release foot pedal so as to adjust the degree of opening of the release valve, whose maximum opening area is made relatively large. However, this is possible in practice only when the release valve is of the screw-operated type, and it is extremely difficult to adjust the degree of opening of the release valve by the pressure release foot pedal because the release valve is generally fully opened when the bearing plate is lowered. Therefore, the opening area of the release valve must be determined as a compromise between the lowering speeds in gradually and rapidly lowering the bearing plate.

Furthermore, the flow rate of the working liquid under pressure flowing into the reservoir is subject to change, depending upon the load exerted on the bearin g plate, so that the bearing plate lowering speed is dependent upon the load exerted on the bearing plate. However, the prior art hydraulic jack cannot adjust its bearing plate lowering speed depending upon the load exerted on the bearing plate. That is, the lowering speed becomes too slow when a load exerted on the bearing plate is ligher than the maximum load from which a reference lowering speed is determined. On the other hand, when a lighter load is used to determine a reference lowering'speed, the bearing plate is lowered too suddenly when a heavy load is exerted on it.

SUMMARY OF THE INVENTION One of the objects of the present invention is to provide an improved hydraulic jack for use in a garage having a lift arm and a bearing plate which can be low ered at two speeds when a pressure release foot pedal is applied in two steps so that, depending upon a load, a high or low lowering speed may be selected.

According to one aspect of the present invention, two release valves of respectively a small and large discharge capacities are disposed in parallel between a working oil supply and discharge passages of a hydraulic cylinder for raising and lowering a lift arm and hence a bearing plate in such a manner that the small capacity release valve is operatively connected to a pressure release foot pedal so as to be opened when the foot pedal is partially depressed, whereas the large capacity release valve has its actuating member operatively coupled to the pressure release foot pedal so as to be opened when the foot pedal is fully depressed. Therefore, when the foot pedal is applied, the small capacity release valve is opened first, and when the foot pedal is fully applied, the large capacity release valve is also opened so that the flow rate of the working fluid under pressure discharged from the hydraulic cylinder is varied in two steps. As a consequence, the speed in lowering the lift arm and hence the bearing plate can be varied in two steps, that is at slow and high lowering speeds.

According to another aspect of the present invention, an adjusting screw is interposed between the small and large capacity release valves so that when the foot pedal is fully depressed, the opening area of the large capacity release valve can be adjusted to freely adjust the lowering speed depending upon a load applied on the bearing plate.

According to another aspect of the present invention, a safety valve or pressure relief valve is incorporated in the large capacity release valve, and is directly communicated with a pump chamber so that when the pressure of the working fluid in the pump chamber rises in excess of a predetermined level, the relief valve is opened to directly return the working fluid under pressure from the pump chamber to the reservoir without flowing into the hydraulic cylinder.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view partly in section of a hydraulic jack in accordance with the present invention;

FIG. 2 is a front view thereof;

FIG. 3 is a longitudinal sectional view, on enlarged scale, of a hydraulic cylinder and a valve mechanism thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a side view thereof;

FIG. 6 is a sectional view taken along the line of 6-6 of FIG. 3; and

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, a carriage generally designated by reference numeral comprises two shaped or angle members disposed in parallel with and joined to each other by front and rear shafts 11 and 12 which carry front and rear wheels 13 and 14, respectively. A lift arm 16 comprising a channel-like member is pivotably fixed on a shaft to the carriage l0, and a load bearing plate 18 is rotatably fixed to the upper end of the lift arm 16. The upper and lower ends of parallel links 19 are pivoted to the bearing plate 18 and the carriage 10, respectively, with pins 20 and 21, and the links 19, the lift arm 16 and the bearing plate 18 constitute a parallel linkage, whereby the bearing plate 18 may be normally maintained horizontal irrespective of the rotation of the lift arm 16 about the pivot 15. The rotation of the lift arm 16 can be effected by a hydraulic cylinder 22 mounted on the rear portion of the carriage 10, and a by driving mechanism generally designated by and comprising a valve mechanism 23 and a pump mechanism 24 for actuating the hydraulic cylinder 22.

The driving mechanism 25 is fixed to the carriage by arms 26 extending from both sides of the valve mechanism 23, and by screws 27 or the like. The extreme end of a ram 28 of the hydraulic cylinder 22 is connected to a connecting plate 30 which interconnectes the ends of links 29. That is, the extreme end of the ram 28 is connected to the connecting plate 30 with a connecting pin 32 fitted into a hole 31 formed in the plate 30. The other ends of the links 29 are connected by pivot pins 33 to the lower end of the lift arm 16 so that, when the ram 28 is extended, the lift arm 16 is rotated upwardly about its pivot pin 15. The lift arm 16 may be lowered under the returning force of a spring 34 acting between the connecting plate 30 and the shaft 12 of the carriage l0, whil the ram 28 is retracted.

Next referring to FIGS. 3 5, the hydraulic cylinder 22, the valve mechanism 23 and the pump mechanism 24 are assembled into a unitary construction by welding or the like with the valve mechanism 23 interposed between the pump mechanism 24 and the hydraulic cylinder 22 as best seen in FIG. 4. The hydraulic cylinder 22 has a double-cylinder construction comprising a cylinder 35 and a cover or outer casing 36 surrounding the cylinder 35 as best seen in FIG. 3, to define a tank chamber 37 therebetween. The ram 28 is slidably fitted into the cylinder 35.

An opening or bore 38 is open at the end of the ram 28, and an opening or bore 39 of oval section is formed at a right angle to the opening 38. A valve 41 fitted into the bore 38 normally closes the bore 38 under the force of a spring also fitted into the bore 38, and an actuating rod 43 is looselyfitted into the bore 39. The actuating rod 43 has a pin 42 which extends through a communication passage between the bores 38 and 39 to ward the valve 41.

When the ram 28 is extended to the extreme end of its stroke under the force of liquid under pressure which is introduced into a lower chamber 44 in the cylinder 35, both the upper and lower ends of the actuating rod 43 engage with a bearing member 45 fitted into the cylinder 35, and are caused to be displaced toward the left in FIG. 3 in the bore 39. As a result, the pin 42 causes the valve 41 to open so that the lower chamber 44 communicates through the bore 38, the oval bore 39, the space 46 between the cylinder 45 and the ram 28 and an opening 47 formed in the cylinder 35 near the opening end thereof, with the chamber 37. As a result, the oil under pressure is returned from the lower chamber 44 to the tank chamber 37.

Therefore, when the ram 28 reaches the extreme end of its stroke, the pressure in the lower chamber is reduced immediately. This arrangement is very advantageous in that when the ram is fully extended, the forces exerted on the base thereof and on the portion of the cylinder 35 near its opening end are reduced.

The pump mechanism 24 comprises a manually operated plunger pump having a pump cylinder 48 and a plunger 49 slidably fitted into the pump cylinder 48. As the plunger 49 reciprocates, the working oil or fluid is drawn into the pump cylinder 48 through a suction passage 50 formed in the valve mechanism 23 and a suction valve 51 inserted in the passage 50 from the tank chamber 37 of the hydraulic cylinder 22, the working fluid being forced into the lower chamber 44 of the hydraulic cylinder 22 through a discharge valve 52 and a supply passage 53 formed in the valve mechanism 23. For this purpose, a communication passage 54 extending from the bottom of the pump cylinder 48 opens at the midpoint between the suction and discharge valves 51 and 52.

Referring back to FIG. 1, in order to reciprocate the plunger 49 of the plunger pump, a pin 59 extending from one end of a swing arm 58 which is pivotally mounted with a pivot pin 57 to the carriage 10, is fitted into a notch 55 of a guide 56 affixed to the free end of the plunger 49. The other or upper end of the swing arm 58 is pivoted via a pivot pin 60 to an operating lever generally designated by 61. The oscillation of the operating lever 61 about the pivot 60 is limited because the lower end 62 of the operating lever 61 engages with shoulders 63 and 64 of the swing arm 58. In order to maintain the joint between the lower end of the lever 61 and the swing arm 68 at these extreme positions, a ball 65 is disposed to engage the either of notches or stepped portions 67 and 68 0f the end 62 of the operating lever 61, under the force of a spring 66. When the operator swings the operating lever 61, the swing arm 58 rotates about the pivot 57 so that the pin 59 attached to the lower end of the swing arm 58 in engagement with the notch 55 of the guide 56 causes it to reciprocate. Thus, the plunger 49 is reciprocated in the pump cylinder 48. When the operating lever 61 is rotated toward the left extreme end in FIG. 1, and the force is applied thereto, the ball 65 is released from the notch 67 so that the operating lever 61 is lowered forwardly until the lower end 62 is in engagement with the shoulder 64 of the swing arm 58, and the ball 65 is in engagement with the notch 65 of the lower end 62 of the operating lever 61. Thus, the operating lever 61 may be maintained in storage position in parallel with the carriage 10 as indicated by the chain lines in FIG. 1.

Still referring to FIG. 1, the operating lever 61 is shown as comprising a rod 69 telescopically fitted into a cylinder 70. When the operating lever 61 is extended, that is, when the cylinder 71 is extended, it may be locked in position by a snap ring fitted over the rod 69 for operation. The cylinder 71 can be retracted to inoperative or storage position at which the length of the operating lever 61 becomes substantially equal to that of the carriage. This arrangement much facilitates the operation and storage of the operating lever 61.

In reciprocation of the guide 56 and hence of the plunger 49, the compression stroke can be limited because the guide 56 engages with the opening end of the pump cylinder 48, whereas the suction stroke can be limited as a stop 72 attached to the swing arm 58 engages with a stopper pin 73 extending from the carriage 10.

Referring back to FIG. 3, the valve mechanism 23 interposed between the hydraulic cylinder 22 and the pump mechanism 24 incorporates a stepped release valve device comprising two release valves 75 and 76 of small and large capacities, respectively, which are in communication with the supply passage 53. These release valves 75 and 76 are actuated a stepped manner to be described in more detail hereinafter.

The small release valve 75 is disposed immediately above the discharge valve 52 in a bore 78 formed in the lower end of a valve case 77 screwed into a valve body 74. The bore 78 is open to the passage 51, and is in communication with the tank chamber 37 of the hydraulic cylinder 22 through a valve bore 79, a bore 80 in the valve case 77, radial bores 81 of the valve case 77 an annular groove 82 formed around the valve case 77, and a discharge passage formed in the valve body 74 (See FIG. 6).

The small release valve 75 is normally pressed against the lower end of the valve bore 79 under the force of a spring 85 which is stressed between the small release valve 75 and a spring seat 84 at the lower end of the valve case 77, so that the communication between the oil supply passage 53 and the tank chamber 37 is interrupted.

A push rod 86 for opening the small release valve 75 is fitted into the upper bore 80 of the valve case 77. The push rod 86 comprises a rod portion 87 extending from the lower end of the push rod 86 toward the upper end of the small release valve 75, and an upper rod portion 88 extending from the upper surface of the push rod 86. A lower spring seat 89 is fitted over the upper small diameter rod portion 88, whereas an upper spring seat 90 is screwed to the upper end of the rod portion 88 to dispose, and a spring 91 is disposed between these upper and lower spring seats 89 and 90.

The lower spring seat 89 has such a diameter that it may be pressed to both the upper ends of the valve case 77 and the push rod 86. That is, the outer diameter of the lower spring seat 89 is made larger than that of the push rod 86 so that the push rod 86 may be maintained in a predetermined position under the force of the spring 91.

The large release valve 76 is interposed between the lower end of a valve case 92 inserted in the valve body 84 in parallel with the valve case 77 and the oil supply passage 53. When the large reease valve 76 is opened, the oil under pressure is forced into the tank chamber 37 of the hydraulic cylinder 22 from an annular chamber 93 (see FIG. 6) formed around the lower portion of the valve case 93, through the discharge passage 83.

A first lever 94 and a second lever 95 are pivotably fixed to a bracket 96 formed at the top of the valve body 74, with a common pivot pin 97 for actuating the small and large release valves 75 and 76 independently. As best shown in FIG. 1, the first lever 94 extends backwardly downwardly of the carriage 10, and has a horizontal extension 98 having a pressure release pedal 99 which serves also as a hanger. A plug 100 is screwed to the upper end of the first lever 94, and a ball 101 is interposed between the plug 100 and the upper end of the upper rod portion 88 of the small release valve 75. When the first lever 94 is rotated about the pivot 97 depressing the pressure release pedal 99 by a foot of a user, the push rod 86 is forced to move downwardly against the spring 91 so that the small diameter lower rod portion 87 is extended beyond the lower end of the valve bore 89 to open the small release valve 75. In order to prevent the force exerted by the first lever 94 from being applied to the push rod 86 as an eccentric load, the ball 101 is interposed between the first lever 94 and the push rod 86.

At one end of the second lever 95 which is also rotated about the pivot 97, there is disposed an adjusting screw 102 extending downwardly to the upper end of the valve case 92 of the large release valve 76. An opening 103 which is formed at the other end of the second lever 95 extending below the first lever 94 over the push rod 86 of the small release valve 75, is fitted loosely around the upper spring of the push rod 86 with a sufficient spacing therebetween, and a spring 104 is stressed between the other end of the second lever and the valve body 74 so that the adjusting screw 102 at the one end of the second lever 95 exerts pressure on the valve case 92 of the large valve case 76 under the force of the spring 104 against a spring 105 fitted over the lower reduced diameter portion of the valve case 92, thereby closing the large release valve 76.

The first and second levers 94 and 95 are spaced apart from each other by an appropriate distance. When the pressure-release foot pedal 99 is partially depressed, only the push rod 86 is moved downwardly to open only the small release valve 75. When the pressure-release foot pedal 99 is further depressed, the undersurface of the first lever 94 engages with the second lever 95 to cause the latter to move downwardly against the spring 104. As a result, the adjusting screw 102 is released from the valve case 92, so that the valve case 92 is lifted under the force of the spring 105. Therefore, the large release valve 76 is now also opened.

The stroke at which the first lever 94 engages with the second lever 95 can be adjusted by the plug when it is appropriately rotated. Therefore, the time when the large release valve 76 is opened after the small release valve 75 can be appropriately adjusted. Since the foot pedal 99 can be fully depressed until the second lever 95 engages with the valve body 74, the degree of opening of the large release valve when the pressure release valve 99 is fully deoressed can be adjusted by rotating the adjusting screw 102.

From the foregoing description, it is seen that the present invention provides a movable hydraulic jack having a stepped release valve device comprising the small and large release valves 75 and 76. According to the present invention, oil under pressure higher than a predetermined level is not forced into the hydraulic cylinder 22 when a load in excess of a predetermined loadis exerted on the lift arm 16, for which purpose a safety device for returning the oil under pressure directly from the pump mechanism 24 to the tank chamber 37 is incorporated in the valve case 92 of the large release valve 76. That is, a valve lock 106 is screwed into the valve case 92, and a T-shaped passage 107 is formed in the lower portion thereof, and is in communication with an annular groove 109 formed in the valve case 92 through a transverse or radial passage 108 formed in the valve lock 106. As shown in FIG. 7, the annular groove 109 is in communication with the pump cylinder 48 through the communication passage 110 formed in the valve body 74. A relief valve 111 is disposed at the junction of the vertical and horizontal passage of the T-shaped passage 107, and is normally pressed against the lower end of the vertical passage thereof under the force of a spring 1 13. As a result, the passage 107 is normally closed so that the oil under pressure supplied from the pump cylinder is stopped. However, when the relief valve 111 is opened, the oil under pressure is returned to the tank chamber through the axial groove formed in the side wall of a relief valve holder 112, an opening 115 formed through the valve case 92 at the lower portion thereof, an annular chamber 93 defined between the reduced diameter portion of the valve case 92, and the discharge passage 83. Therefore, when oil under pressure in excess of a predetermined lever is to be forced into the hydraulic cylinder 22 from the pump cylinder 48, the relief valve 11 1 is opened so that the oil under this excess pressure of a is returned to the tank chamber 37. As a result, no oil under pressure in excess of a predetermined level is forced into the hydraulic cylinder 23, whereby the latter is safeguard against the effects of such excess pressure.

Since the relief valve 111 is incorporated in the large release valve assembly as described above, no additional safety device is required to be installed between the oil supply and discharge passages 53 and 83. This arrangement is advantageous in that the hydraulic circuit can be simple in construction. Furthermore, according to the present invention, the oil under pressure is channelled from the pump cylinder 48 to the relief valve 1 1 1 directly, so that the latter can be immediately opened in response to the increase of the pressure of the working oil in excess of a predetermined level. Thus, a highly sensitive and very reliable safety device is provided.

Next, referring back to FIG. 1, a cover 117 is hinged with a pin 116 to the carriage to cover the adjusting plug 100 and the adjusting screw 102 of the valve mechanism 23. Another cover 118 is provided which extends backwardly of the carriage 10 to cover the pressure release pedal 99 in order to prevent the latter from being depressed by error in operation.

The movable hydraulic jack in accordance with the present invention is adapted to be suspended at the pressure release pedal as described hereinbefore. As a result, the air entrapped in the tank chamber 37 moves into the suction passage 50. Therefore, air would be drawn into the pump cylinder 48 instead of the working oil, and would mix with the working oil. To overcome this problem according to the present invention, a suction pipe 120 having a filter 119 fixed at its free end is extended into the tank chamber from the suction passage 50 as shown in FIG. 3. The filter 119 is always in the working oil in the tank chamber 37 even when the hydraulic jack is suspended so that the intrusion of the air into the suction passage 50 can be positively prevented.

Next the mode of operation will be described hereinafter. The hydraulic jack in accordance with the present invention can be transported while being suspended in a manner described above, to a desired position.

Next the operating lever 61 is raised to extend the cylinder to its full extent, and is used to insert the hydraulic jack below an automobile or the like to be lifted. This can be facilitated as the carriage 10 is provided with the wheels 13 and 14.

When the operating lever 61 is swung, the swing arm 58 oscillates about the pivot 57, whereby the plunger 49 of the pump mechanism 24 reciprocates in the pump cylinder 48 so that the working oil in the tank chamber 37 of the hydraulic cylinder 23 is suctioned into the pump cylinder 48 through the suction pipe 12, the suction passage 50, and the suction valve 51. Thereafter, the oil under pressure is introduced from the pump mechanism 24 to the lower chamber 44 of the hydraulic cylinder 22 through the discharge valve 52 and the oil supply passage 53. As a result, the ram 28 is extended from the cylinder 35, whereby the lower end of the lift arm 16 is moved to the right in FIG. 1 by the links 29 and the connecting plate 30. As a consequence, the lift arm 16 is rotated about the pivot 15 in the direction indicated by the arrow A in FIG. 1. The bearing plate 18 attached to the upper end of the lift arm 16 is lifted while it is maintained in horizontal position by the parallel links 19, whereby the automobile or the like is lifted.

The load exerted on the bearing plate 18 acts as a resisting force on the ram 28 through the links 29 and the connecting plate 30, so that the pressure of the working oil in the pump cylinder 48 is increased in proportion to the load. The pressure of the working oil in the pump cylinder 48 is exerted on the relief valve 111 through the communication passage 110, the annular groove 109, the port 109, and the passage 107 so that if a load in excess of a predetermined level is exerted on the bearing plate 18, the oil under pressure from the pump cylinder 48 opens the relief valve 111 so that the oil under pressure is returned to the tank chamber directly through the axial groove 114 of the valve holder 122, the port or opening 115, the annular chamber 93 and the discharge passage 83 without flowing into the lower chamber 44 of the hydraulic cylinder 22. Therefore, even when the plunger 49 is reciprocated by the operating lever 61, the ram 28 of the hydraulic cylinder 22 is not actuated, whereby the lift arm 16 is maintained at the same height.

When the ram 28 is fully extended to lift the lift arm 16, the actuating rod 43 engages with the bearing member 45 to be displaced toward the left in FIG. 1 so that the pin 42 is caused to displace to the left to open the valve 41. As a consequence, even when the operating lever 61 is actuated, the oil under pressure from the pump cylinder 48 is returned to the tank chamber through the port 38, the valve 41, the oval bore 39 and the port 47. Therefore the pressure of the working oil in the lower chamber 44 is maintained at a lower level. Therefore, the various part in the hydraulic cylinder can be prevented from being subjected to excess forces. In this case, the pressure of the working oil may be set to be less than the pressure at which the relief valve 111 is opened, so that the base portion of the ram 28 and the bearing member 45 at the opening end of the cylinder 35 may have relatively low strength.

When it is desired to lower the lift arm 16 after it has been raised to a desired position, the pressure-release pedal 99 is depressed by half of the full stroke. Then the first lever 94 rotates about the pivot pin 97, and the plug 100 pushes the push rod 86 downwardly. As a result, the rod portion 87 opens the small release valve 75, so that the oil under pressure in the lower chamber 44 of the hydraulic cylinder 22 flows gradually to the tank chamber 37 through the oil supply passage 53, the lower bore 78 in the valve case 77, the valve bore 79 which is constricted, the upper bore 80, the radial bores 81 and the discharge port 83. Therefore, the bearing plate 18 and the lift arm 16 are gradually lowered to a desired position. When the bearing plate 18 reaches this desired position, the foot is released from the pressure-release pedal 99. Then the push rod 86 is returned to its initial position under the force of the spring 91, whereby the small release valve 75 is closed. Thus, the bearing plate 18 maintained in the desired position.

When it is desired to quickly lower the bearing plate 18, the pressure release pedal 99 is depressed by its full stroke. The, the plug 100 of the first lever 94 pushes downwardly the push rod 86 to open the small release valve 75. When the first lever 94 engages with the second lever 95, the latter is caused to rotate about the pin 97 against the spring 104 so that the valve case 92 is raised under the force of the spring 105 to open the large release valve 76 in the manner described hereinbefore. Therefore the working oil under pressure in the lower chamber 44 of the hydraulic cylinder 22 is quickly returned to the tank chamber 37 not only through the small release valve 75 but also through the large release valve 76, the annular chamber 93 and the discharge passage 83. As a result, the bearing plate 18 can be quickly lowered.

So far the preferred embodiment of the present invention has been described, but it is understood that various modifications and variations can be effected without departing from the scope of the present invention.

What is claimed is:

1. A hydraulic jack for use in garages, comprising a carriage;

a lift arm mounted on said carriage for displacement between raised and lowered positions;

a hydraulic cylinder also mounted on said carriage and having an extensible ram associated with said lift arm for raising and lowering of the same;

a pump mechanism for supplying hydraulic pressure fluid into said cylinder;

valvemeans communicating with said cylinder for discharging hydraulic pressure fluid therefrom,

said valve means comprising a normally closed first valve operable for discharging said hydraulic pressure fluid from said cylinder at a first rate,

and a normally closed second valve for discharging said hydraulic pressure fluid from said cylinder at a faster second rate;

and actuating means for said valves, comprising an arm mounted for pivoting movement,

a first portion associated with said arm and said first valve and operative for opening the latter when said arm is pivoted in a given direction and through a given distance,

and a second portion associated with said first portion and said second valve and operative for opening said second valve when said arm is pivoted in said given direction beyond said given distance.

2. A hydraulic jack as defined in claim 1, wherein said actuating means is provided with a foot pedal.

3. A hydraulic jack as defined in claim 1; further comprising adjusting means for adjusting the distance through which said arm is to be pivoted beyond said given distance for opening of said second valve.

4. A hydraulic jack as defined in claim 3, wherein said adjusting means is interposed between said first portion and said first valve.

5. A hydraulic jack as defined in claim 3, wherein said second valve is adjustable; and further comprising additional adjusting means for adjusting said second valve so as to vary said second rate of hydraulic pressure fluid discharged from said cylinder.

6. A hydraulic jack as defined in claim 1; and further comprising safety valve means incorporated in said second valve means,

7. A hydraulic jack as defined in claim 1; and further comprising safety valve means incorporated in said second valve means and actuatable in response to the pressure of said hydraulic pressure fluid in said pump mechanism exceeding a preset level.

8. A hydraulic jack as defined in claim 1; further comprising a reservoir partially filled with hydraulic pressure fluid and partially filled with air, said pump mechanism communicating with said reservoir for receiving hydraulic pressure fluid therefrom; and means for preventing air from said reservoir from entering into said pump mechanism. 

1. A hydraulic jack for use in garages, comprising a carriage; a lift arm mounted on said carriage for displacement between raised and lowered positions; a hydraulic cylinder also mounted on said carriage and having an extensible ram associated with said lift arm for raising and lowering of the same; a pump mechanism for supplying hydraulic pressure fluid into said cylinder; valve means communicating with said cylinder for discharging hydraulic pressure fluid therefrom, said valve means comprising a normally closed first valve operable for discharging said hydraulic pressure fluid from said cylinder at a first rate, and a normally closed second valve for discharging said hydraulic pressure fluid from said cylinder at a faster second rate; and actuating means for said valves, comprising an arm mounted for pivoting movement, a first portion associated with said arm and said first valve and operative for opening the latter when said arm is pivoted in a given direction and through a given distance, and a second portion associated with said first portion and said second valve and operative for opening said second valve when said arm is pivoted in said given direction beyond said given distance.
 2. A hydraulic jack as defined in claim 1, wherein said actuating means is provided with a foot pedal.
 3. A hydraulic jack as defined In claim 1; further comprising adjusting means for adjusting the distance through which said arm is to be pivoted beyond said given distance for opening of said second valve.
 4. A hydraulic jack as defined in claim 3, wherein said adjusting means is interposed between said first portion and said first valve.
 5. A hydraulic jack as defined in claim 3, wherein said second valve is adjustable; and further comprising additional adjusting means for adjusting said second valve so as to vary said second rate of hydraulic pressure fluid discharged from said cylinder.
 6. A hydraulic jack as defined in claim 1; and further comprising safety valve means incorporated in said second valve means,
 7. A hydraulic jack as defined in claim 1; and further comprising safety valve means incorporated in said second valve means and actuatable in response to the pressure of said hydraulic pressure fluid in said pump mechanism exceeding a preset level.
 8. A hydraulic jack as defined in claim 1; further comprising a reservoir partially filled with hydraulic pressure fluid and partially filled with air, said pump mechanism communicating with said reservoir for receiving hydraulic pressure fluid therefrom; and means for preventing air from said reservoir from entering into said pump mechanism. 